'\" et
.TH MQ_SEND "3P" 2017 "IEEE/The Open Group" "POSIX Programmer's Manual"
.\"
.SH PROLOG
This manual page is part of the POSIX Programmer's Manual.
The Linux implementation of this interface may differ (consult
the corresponding Linux manual page for details of Linux behavior),
or the interface may not be implemented on Linux.
.\"
.SH NAME
mq_send,
mq_timedsend
\(em send a message to a message queue (\fBREALTIME\fP)
.SH SYNOPSIS
.LP
.nf
#include <mqueue.h>
.P
int mq_send(mqd_t \fImqdes\fP, const char *\fImsg_ptr\fP, size_t \fImsg_len\fP,
    unsigned \fImsg_prio\fP);
.P
#include <mqueue.h>
#include <time.h>
.P
int mq_timedsend(mqd_t \fImqdes\fP, const char *\fImsg_ptr\fP, size_t \fImsg_len\fP,
    unsigned \fImsg_prio\fP, const struct timespec *\fIabstime\fP);
.fi
.SH DESCRIPTION
The
\fImq_send\fR()
function shall add the message pointed to by the argument
.IR msg_ptr
to the message queue specified by
.IR mqdes .
The
.IR msg_len
argument specifies the length of the message, in bytes, pointed to by
.IR msg_ptr .
The value of
.IR msg_len
shall be less than or equal to the
.IR mq_msgsize
attribute of the message queue, or
\fImq_send\fR()
shall fail.
.P
If the specified message queue is not full,
\fImq_send\fR()
shall behave as if the message is inserted into the message queue at
the position indicated by the
.IR msg_prio
argument. A message with a larger numeric value of
.IR msg_prio
shall be inserted before messages with lower values of
.IR msg_prio .
A message shall be inserted after other messages in the queue, if any,
with equal
.IR msg_prio .
The value of
.IR msg_prio
shall be less than
{MQ_PRIO_MAX}.
.P
If the specified message queue is full and O_NONBLOCK
is not set in the message queue description associated with
.IR mqdes ,
\fImq_send\fR()
shall block until space becomes available to enqueue the message, or
until
\fImq_send\fR()
is interrupted by a signal. If more than one thread is waiting to send
when space becomes available in the message queue and the Priority
Scheduling option is supported, then the thread of the highest priority
that has been waiting the longest shall be unblocked to send its
message. Otherwise, it is unspecified which waiting thread is
unblocked. If the specified message queue is full and O_NONBLOCK is
set in the message queue description associated with
.IR mqdes ,
the message shall not be queued and
\fImq_send\fR()
shall return an error.
.P
The
\fImq_timedsend\fR()
function shall add a message to the message queue specified by
.IR mqdes
in the manner defined for the
\fImq_send\fR()
function. However, if the specified message queue is full and
O_NONBLOCK is not set in the message queue description associated with
.IR mqdes ,
the wait for sufficient room in the queue shall be terminated when the
specified timeout expires. If O_NONBLOCK is set in the message queue
description, this function shall be equivalent to
\fImq_send\fR().
.P
The timeout shall expire when the absolute time specified by
.IR abstime
passes, as measured by the clock on which timeouts are based (that is,
when the value of that clock equals or exceeds
.IR abstime ),
or if the absolute time specified by
.IR abstime
has already been passed at the time of the call.
.P
The timeout shall be based on the CLOCK_REALTIME clock.
The resolution of the timeout shall be the resolution of the clock on
which it is based. The
.IR timespec
argument is defined in the
.IR <time.h> 
header.
.P
Under no circumstance shall the operation fail with a timeout if there
is sufficient room in the queue to add the message immediately. The
validity of the
.IR abstime
parameter need not be checked when there is sufficient room in the
queue.
.SH "RETURN VALUE"
Upon successful completion, the
\fImq_send\fR()
and
\fImq_timedsend\fR()
functions shall return a value of zero. Otherwise, no message shall be
enqueued, the functions shall return \-1, and
.IR errno
shall be set to indicate the error.
.SH ERRORS
The
\fImq_send\fR()
and
\fImq_timedsend\fR()
functions shall fail if:
.TP
.BR EAGAIN
The O_NONBLOCK flag is set in the message queue description associated
with
.IR mqdes ,
and the specified message queue is full.
.TP
.BR EBADF
The
.IR mqdes
argument is not a valid message queue descriptor open for writing.
.TP
.BR EINTR
A signal interrupted the call to
\fImq_send\fR()
or
\fImq_timedsend\fR().
.TP
.BR EINVAL
The value of
.IR msg_prio
was outside the valid range.
.TP
.BR EINVAL
The process or thread would have blocked, and the
.IR abstime
parameter specified a nanoseconds field value less than zero or greater
than or equal to 1\|000 million.
.TP
.BR EMSGSIZE
The specified message length,
.IR msg_len ,
exceeds the message size attribute of the message queue.
.TP
.BR ETIMEDOUT
The O_NONBLOCK flag was not set when the message queue was opened, but
the timeout expired before the message could be added to the queue.
.LP
.IR "The following sections are informative."
.SH EXAMPLES
None.
.SH "APPLICATION USAGE"
The value of the symbol
{MQ_PRIO_MAX}
limits the number of priority levels supported by the application.
Message priorities range from 0 to
{MQ_PRIO_MAX}\-1.
.SH RATIONALE
None.
.SH "FUTURE DIRECTIONS"
None.
.SH "SEE ALSO"
.IR "\fImq_open\fR\^(\|)",
.IR "\fImq_receive\fR\^(\|)",
.IR "\fImq_setattr\fR\^(\|)",
.IR "\fItime\fR\^(\|)"
.P
The Base Definitions volume of POSIX.1\(hy2017,
.IR "\fB<mqueue.h>\fP",
.IR "\fB<time.h>\fP"
.\"
.SH COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1-2017, Standard for Information Technology
-- Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 7, 2018 Edition,
Copyright (C) 2018 by the Institute of
Electrical and Electronics Engineers, Inc and The Open Group.
In the event of any discrepancy between this version and the original IEEE and
The Open Group Standard, the original IEEE and The Open Group Standard
is the referee document. The original Standard can be obtained online at
http://www.opengroup.org/unix/online.html .
.PP
Any typographical or formatting errors that appear
in this page are most likely
to have been introduced during the conversion of the source files to
man page format. To report such errors, see
https://www.kernel.org/doc/man-pages/reporting_bugs.html .
